HTML button onclick
<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>
<body>
<p>There is a hidden message for you. Click to see it.</p>
<button onclick="myFunction()">Click me!</button>
<p id="demo"></p>
<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Hello Dear Visitor!</br> We are happy that you've chosen our website to learn programming languages. We're sure you'll become one of the best programmers in your country. Good luck to you!";
}
</script>
</body>
</html>